arm: socfpga: Convert Altera DDR SDRAM driver to use Kconfig

Convert Altera DDR SDRAM driver to use Kconfig method.
Enable ALTERA_SDRAM by default if it is on Gen5 target.
Arria 10 will have different driver.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
diff --git a/drivers/ddr/altera/Kconfig b/drivers/ddr/altera/Kconfig
new file mode 100644
index 0000000..021ec1d
--- /dev/null
+++ b/drivers/ddr/altera/Kconfig
@@ -0,0 +1,5 @@
+config ALTERA_SDRAM
+	bool "SoCFPGA DDR SDRAM driver"
+	depends on TARGET_SOCFPGA_GEN5
+	help
+	  Enable DDR SDRAM controller for the SoCFPGA devices.